An upper bound for the conditioning of the preconditioned system [1]} is
\(k\left( \mathcal {M}^{-\frac{1}{2}}_{\text{ad}}\mathbf {M}\mathcal {M}^{-\frac{1}{2}}_{\text{ad}}\right) \le C N_{\mathrm {adj}}^2,\) 
